MODULE 9 - exercise physiology

evidence indicates that one fiber type can actually be converted to the other type

(e.g. type I to type II, or vise versa) as a result of cross-innervation or chronic stimulation, and possibly with training

Strength training for older adults, females, and youth. Can and should each of these special populations perform resistance training?

***

What are the specific neural changes that occur with resistance training?

*** One of the neural changesthat occurs has to do with motor unit recruitment. Pay attention to synchronous and asynchronous motor unit recruitment.

Strength gains may also result from greater motor unit recruitment

- increase in Neural drive during maximal contraction - increase in Frequency of neural discharge causes rate coding - decrease in Inhibitory impulses

•After 3 to 6 months of resistance training

-25 to 100% strength gain •Results may seem misleading -Learn to more effectively produce force -Learn to produce true maximal movement

Resistance Training for Special Populations: elderly

-Helps restore age-related loss of muscle mass -Improves quality of life and health

Fiber Hyperplasia in cats

-Intense strength training (high load/low reps) -Each half grows to size of parent fiber

Fiber Hyperplasia in chickens, mice, rats

-Intense strength training (low load/ high reps) -But difference may be due to training regimen

Fiber Hyperplasia in humans

-Most hypertrophy due to fiber hypertrophy -Fiber hyperplasia also contributes -Fiber hypertrophy versus fiber hyperplasia may depend on resistance training intensity/load -Higher intensity ----> (type II) fiber hypertrophy

Fiber hyperplasia - satellite cells

-Myogenic stem cells involved in muscle regeneration -Activated by stretch, injury, or muscle injury After activation, cells proliferate, migrate, fuse

Resistance Training for Special Populations: children and adolescents

-Myth: resistance training unsafe due to growth plate, hormonal changes -Truth: safe with proper safeguards -Children can gain both strength and muscle mass

•Testosterone facilitates fiber hypertrophy

-Natural anabolic steroid hormone -Synthetic anabolic steroids causes large increases in muscle mass •However, these hormonal increases have been shown not to be necessary to stimulate muscle anabolism

Chronic hypertrophy (long term)

-Reflects actual structural change in muscle -Fiber hypertrophy, fiber hyperplasia, or both

•Strength gains similar as a percent of initial strength

-Young men experience greatest absolute gains versus young women, older men, children -Due to incredible muscle plasticity

Let's examine the neural and muscular mechanisms that bring about gains in muscular strength. The specific neural adaptations that lead to initial increases in strength are:

1 Synchronization of motor units 2 Increased motor unit recruitment 3 Increased neural drive 4 Autogenic inhibition 5 Reduced coactivation of agonist and antagonist muscles

Daily recommendations for protein intake to facilitate protein synthesis is equal to

1.6 to 1.7 grams of protein per kilogram of body weight per day. For a 150-pound person that would be approximately 110 to 115 grams of protein per day. For reference, 8 ounces of yogurt contains approximately 11 grams of protein, while a quarter pound of meat contains approximately 29 grams of protein. In addition, 20 to 25 grams of protein after resistance exercise will enhance protein synthesis.

Type I

Aerobic Capacity: high Anaerobic Capacity: low Contraction Speed: slow Fatigue Resistance: high Myoglobin Content: high Glycogen Content: low Color: red

Type IIB

Aerobic Capacity: low Anaerobic Capacity: high Contraction Speed: fast Fatigue Resistance: low Myoglobin Content: low Glycogen Content: high Color: white

Type IIA

Aerobic Capacity: moderate/high Anaerobic Capacity: high Contraction Speed: fast Fatigue Resistance: moderate/high Myoglobin Content: high Glycogen Content: moderate Color: reddish/white

Autogenic Inhibition

As previously discussed, the Golgi tendon organ prevents injury by inhibiting force production. This is called autogenic inhibition. While this is mainly a protective mechanism, it can also reduce the maximum force-producing capacity of a muscle. Resistance training can reduce autogenic inhibition and allow for greater muscle force production.

inhibitory mechanisms in the neuromuscular system, such as the Golgi tendon organs, might be necessary to prevent the muscles from exerting more force than the bones and connective tissues can tolerate. This control is referred to as

Autogenic inhibition However- under extreme situations when larger forces are sometimes produced, significant damage can occur to these structures- suggesting that the protective inhibitory mechanisms can be overridden

Resistance training and gender

Females have also been found to improve strength and experience similar hypertrophy as males. Men do achieve a greater absolute increase in muscle size because they have a greater amount of muscle mass to begin with. Initial increases in muscular strength are largely neural, with hypertrophy coming after about three to four weeks of resistance training.

Neural Adaptations: Increased motor unit recruitment

If we recruit many motor units we can produce more force. Resistance training results in more motor units being recruited to get the job done

Resistance training in youth

In a position statement, the National Strength and Conditioning Association (NSCA) said that youth are able to increase strength and muscle mass, and that resistance training is safe and effective for youth and does not negatively impact growth plates. However, the NSCA stresses that the emphasis of a youth resistance training program should be on proper technique and safety.

Change in Muscle Fiber Type

In humans, there is conflicting evidence of change in muscle fiber type with normal resistance training. It is probable that type II fibers, especially type IIA fibers, become more oxidative with aerobic training.

Resistance training causes

Increase in protein synthesis -Muscle protein content always changing -During exercise: synthesis decreases, degradation increases -After exercise: synthesis increases, degradation decreases

Fiber Hyperplasia

Increase in total # of fibers within a muscle

autogenic inhibition

Inhibitory mechanisms in the neuromuscular system such as the golgi tendon organs might be necessary to prevent the muscles from exerting more force than the bones and connective tissues can tolerate however, under extreme conditions when larger forces are sometimes produced - significant damage can occur to these structures, suggesting that the protective inhibitory mechanisms can be overridden

There is an interaction between resistance training and diet.

Muscle hypertrophy and increased strength with resistance training are highly dependent on dietary factors, particularly protein intake. Protein can be synthesized (anabolism) and can be broken down (catabolism). The combination of protein anabolism and catabolism results in protein balance. In order for hypertrophy to occur, protein anabolism must be greater than catabolism resulting in a positive protein balance. During resistance exercise, protein catabolism increases and protein anabolism decreases. As such, protein ingestion is of utmost importance to help with muscle hypertrophy.

Chronic hypertrophy

Refers to the increase in muscle size that occurs with long-term resistance training This reflects actual structural changes in the size of existing individual muscle fibers (muscle hypertrophy), in the number of muscle fibers (fiber hyperplasia), or in both

Reduced Co-Activation of Agonist and Antagonist Muscles

Remember that the agonist is the prime mover in a contraction while the antagonist is the opposing muscle. In a bicep curl, the agonist is the bicep and the tricep is the antagonist. If we were to contract both the bicep and the tricep with equal force, no movement would take place. So to bring about a stronger contraction, it would be beneficial to inhibit neural impulses or to relax the tricep to bring about greater force production in the bicep. Later increases in strength are due to increases in muscle size which could be attributed to two mechanisms--muscle fiber hypertrophy and muscle fiber hyperplasia. But, there's little evidence of fiber hyperplasia under normal circumstances.

Resistance training in older adults

Resistance training is safe for older adults, and it should be an important part of their workout. As adults age, there is a normal decrease in fat free mass due to a reduction in protein synthesis. This is called sarcopenia. Older adults have shown gains in strength and muscle mass, a decrease in falls, and an overall improvement in the quality of life with a resistance training program. The majority of the strength gains in older adults are primarily neural, but there is evidence that older adults do exhibit an increase in muscle size with resistance training. The American College of Sports Medicine guidelines for resistance training for older adults prescribes performing one set of 8 to 12 repetitions of exercises incorporating all major muscle groups. However, research has found that the majority of strength reductions in older adults is due to atrophy of type II fibers. As such, it would seem prudent to include exercises that focus on strength and power which are those that use the type II fibers.

Neural Adaptations: Synchronization of motor units

Sometimes motor units are recruited asynchronously, or not at the same time. Synchronous recruitment, which is all muscle fibers recruited to fire at the same time, provides for a more forceful contraction, increases the capability to exert steady forces, and leads to greater strength gains

TRUE OR FALSE: women respond to resistance training in a way that is similar to men

TRUE

transient muscle hypertrophy

Temporary enlargement of muscle resulting from edema immediately after an exercise bout

Neural Adaptations: Increased neural drive

The neural drive is the combination of motor unit recruitment and the rate at which neural impulses are conducted to the motor units. To increase neural drive, more motor units are recruited which may be the result of greater impulse generation via the motor neurons or the reduction of inhibitory impulses

There are two types of changes or adaptations that occur with resistance training.

There are neural changes and there are muscular changes.

There aretwo ways that muscle fibers can get bigger

There is hypertrophy of muscle fibers and hyperplasia of muscle fibers One absolutely occurs. The other occurs in cats, but not so much in humans. So pay attention to,which is in and which generally occurs with resistance training.

sarcopenia

a substantial loss of fat-free body mass accompanies aging this loss reflects mainly the loss of muscle mass

In conclusion, resistance training is safe and effective and recommended for all, regardless of age or gender. Early increases in muscle strength are largely neural in nature. However

additional increases in strength are due to muscle fiber hypertrophy. As muscle hypertrophy and increased strength gains are highly dependent on a positive protein balance, protein intake is very important for muscle hypertrophy.

resistance trained athletes should consume an adequate amount of high quality protein (as high as 1.7 g/kg of body weight per day)

along with carbohydrate in order to stimulate muscle protein synthesis and also replenish muscle glycogen stores after exercise

neural mechanisms leading to strength gains can include

an increase in frequency if stimulation, or rate coding; recruitment of more motor units; more synchronous recruitment of motor units; and decreases in autogenic inhibition from the golgi tendon organs

Most muscle hypertrophy results from

an increase in the size of individual muscle fibers (fiber hypertrophy)

most muscle hypertrophy results from

an increase in the size of individual muscle fibers (fiber hypertrophy)

Most athletes in most sports can benefit from resistance training fi an appropriate program is assigned to them. But to ensure that the program is working, performance should be

assessed periodically and the training regimen adjusted as needed

muscles decrease in size

atrophy

atrophy begins very quickly if training has stopped, but training can be reduced, as in a maintenance program, without resulting in

atrophy or loss of strength

resistance training can decrease inhibitory impulses to agonist muscles by reducing

autogenic inhibition

muscle atrophy (decrease in size and strength) when they

become inactive, as with injury, immobilization, or cessation of training

atrophy begins very quickly if training is stopped

but training can be reduced, as in maintenance program, without resulting in atrophy or loss of strength

Resistance trained athletes should consume an adequate amount of high-quality protein (as high as 1.7 g per kg of body weight per day) along with ....

carbohydrate in order to stimulate muscle protein synthesis and also replenish muscle glycogen stores after exercise

Fiber hyperplasia may only occur in

certain individuals under certain conditions

Early gains in strength appear to result more from

changes in neural factors, but later long-term gains are largely the result of muscle hypertrophy

fiber hypertrophy increases the numbers of myofibrils and actin and myosin filaments, which provides more

cross-bridges for force production

Evidence indicates that one fiber type can actually be converted to the other type (e.g. type I to type II, or vice versa) as a result of...

cross-innervation or chronic stimulation, and possibly with training

Protein synthesis _______ during exercise, and ___________ after exercise

decreases, increases

immobilization

during the first 6 hours of immobilization, the rate of protein synthesis starts to decrease- likely initiates

transient muscle hypertrophy is the temporary enlargement of muscle resulting from

edema immediately after an exercise bout

motor units are generally recruited asynchronously, they are not all engaged at the same instant - instead, they are controlled by a number of different neurons which transmit

excitatory or inhibitory impulses

TRUE OR FALSE: an athlete training to increase muscle size should eat 20-25 g of protein a day

false

TRUE OR FALSE: asynchronous recruitment of motor units will result in a greater force production than synchronous reqruitment

false

TRUE OR FALSE: transient hypertrophy results from increased protein synthesis and lasts about a week

false

Fiber Hyperplasia can also occur through

fiber splitting

as frequency of stimulation of a given motor unit increases, the muscle eventually reaches a state of tetanus, producing the absolute peak

force or tension if the muscle fiber or motor unit

Neural mechanisms leading to strength gains can include an increase in

frequency of stimulation or rate coding recruitment of more motor units more synchronous recruitment of motor units decreases in autogenic inhibition from the Golgi tendon organs

Both improved motor unit synchronization and motor unit recruitment =

gains

There is significant evidence that muscle fiber _________ occurs with regular resistance training in humans

hypertrophy

Neural adaptations always accompany the strength gains that result from resistance training, but...

hypertrophy may or may not take place

the motor unit is activated and its muscle fibers contract only when

incoming excitatory impulses and threshold is met or exceeded

hypertrophy

increase in muscle size

Mechanisms of Muscle Strength Gain - Hypertrophy versus atrophy

increase in muscle size causes increase muscle strength decrease in muscle size causes decrease muscle strength -Ability to generate force depends on the # of cross-bridges within the sarcomeres -But association more complex than that

chronic hypertrophy

increase in muscle size that occurs with long-term resistance training actual structural changes

Mechanisms of Muscle Strength Gain - Strength gains result from

increase in muscle size? altered neural control

transient hypertrophy textbook

increased muscle size that develops during and immediately following a single exercise bout results mainly from fluid accumulation (edema) in the interstitial and intracellular spaces

transient hypertrophy textbook definition

increased muscle size that develops during and immediately following a single exercise bout. This results mainly from fluid accumulation (edema) in the interstitial and intracellular spaces of the muscle that comes from the blood plasma Lasts only for a short time- the fluid returns to the blood within hours after exercise

The increases in muscle fiber hypertrophy are due to greater protein synthesis resulting from resistance training, which leads to

increased thickness of the myofibrils and corresponding increases in the sarcoplasm increased size of the actin and myosin myofilaments, and increased size and strength of connective tissue

the elderly must consume

larger amounts of protein for same affect

the rate of protein synthesis within the myofibrils is controlled by an enzyme known as

mTOR the primary stimulus for protein synthesis is the mechanical stretch applied to the muscle, which activates mTOR through a signaling factor involving IGF-1

the rate of protein synthesis within the myofibrils by an enzyme known as

mTOR the primary stimulus for protein synthesis is the mechanical stretch applied to the muscle, which activates mTOR through a signaling pathway involving IGF-1

mTOR

mechanistic target of rapamycin the rate of protein synthesis within the myofibrils is controlled primarily by an enzyme, or kinase, known as this. integrated input from upstream pathways, including insulin and growth factors

muscle fiber hypertrophy can be explained by

more myofibrils, actin and myosin filaments, sarcoplasm, connective tissue is prob caused by increase in numbers of myofibrils and actin and myosin filaments, which would provide more cross-bridges for force production during maximal contraction

Another adaptation that occurs with resistance training has to do with the

muscle fibers

RIbosome biogensis, the creation of new ribosomes, appears to be another important mechanism in regulating

muscle hypertrophy in response to resistance exercise

Fiber hypertrophy increases the numbers of

myofibrils and actin and myosin filaments, which provides more cross-bridges for force production

satellite cells

myogenic stem cells involved in skeletal muscle regeneration, are likely involved in the generation of new muscle fibers typically activated by muscle stretching and injury muscle injury results from intense training, particularly eccentric-action training muscle injury can lead to a cascade of responses in which satellite cells become activated and proliferate, migrate to the damaged region, and fuse to existing myofibers or combine and fuse to produce new myofibers

aged skeletal muscle retains the ability to respond to exercise, insulin, and enhanced protein intake to substantially increase

net protein synthesis however, older muscles have a blunted response compared to younger muscles

Strength increases in older populations is primarily due to

neural adaptations

an important contribution to strength gains, especially in early stages of resistance training is

neural adaptations

Increases in muscular strength are brought about by both

neural and muscular mechanisms

Strength is a property of the ___, not just of muscle.

neuromotor system

Resistance training yields substantial strength gains via

neuromuscular changes •Important for overall fitness and health •Critical for athletic training programs

satellite cells provide additional

nuclei within muscle fibers the added genetic machinery (DNA) is necessary to provide the increased muscle protein content and related materials to facilitate hypertrophy (and theoretically, hyperplasia)

Chronic muscle hypertrophy

occurs from repeated resistance training and reflects structural changes in the muscle

aged skeletal muscle retains the ability to respond to exercise, insulin and enhanced protein intake to substantially increase net protein synthesis. however....

older muscles have a blunted response compared to younger muscles

Muscle fiber hyperplasia has been clearly shown to occur in animal models with the use of resistance training to induce muscle hypertrophy

only a few studies suggest evidence of hyperplasia in humans

muscle fiber hyperplasia has been clearly shown to occur in animal models with the use of resistance training to induce hypertrophy

only a few studies suggest hyperplasia in humans

Both muscle hypertrophy and alterations in neural control are contributors to the strength improvements observed in response to resistance training. Changes in neural activation appear to be generally responsible for the early training-induced strength gains up to about six to eight weeks.

owever, muscle hypertrophy is the predominant determinant of further strength gains with continued training.

most athletes in sports can benefit from resistance training if an appropriate program is designed for them but to ensure that the program is working....

performance should be assessed periodically and the training regimen adjusted as needed

Resistance exercise and protein intake are

powerful stimulators of skeletal muscle protein synthesis

resistance exercise and protein intake are

powerful stimulators of skeletal muscle protein synthesis

A major consideration when prescribing resistance training to children and adolescents is

proper training technique

Rapid movement or ballistic-type training may be particularly effective in stimulating increases in motor unit recruitment and...

rate coding

synchronization improves

rate of force development and the capacity to exert steady forces

Ribosome biogenesis, the creation of new ribosomes, appears to be another important mechanism

regulating muscle hypertrophy in response to resistance exercise

chronic muscle hypertrophy occurs from

repeated resistance training and reflects actual structural changes in the muscle

Major neuromuscular adaptations occur with

resistance training

And lastly, protein needs change with

resistance training programs. So you should pay attention to what are the protein needs overall and what are the protein needs right after a resistance training bout.

in elderly people, resistance training can slow or reverse the age-associated loss of muscle mass known as

sarcopenia

loss of muscle mass that accompanies aging is called

sarcopenia

resistance training can benefit almost everyone regardless of

sex age or athletic involvement

resistance training can benefit almost everyone, regardless of

sex, age, or athletic involvement

hormones associated with muscular strength

testosterone, growth hormone and insulin like growth factor

Coactivation of agonists, antagonists muscles

the agonist muscles are the primary movers, the antagonist muscles act to impede the agonists can contribute to strength gain

neural drive

the combination of motor unit recruitment and rate coding od the units starts in the central nervous system and is spread to muscle fibers through peripheral nerves strength gains can be improved by an increase in _______ to the alpha motor units during maximal contraction

increase in neural drive can increase

the frequency of discharge (rate coding) of the motor units or reduce inhibitory impulses, allowing for more motor units to be activated at a higher frequency maximal neural drive appears to increase with resistance training

the increase in neural drive of alpha motor neurons could also increase

the frequency of discharge, or rate coding, of their motor units

early gains in strength appear to result more from changes in neural factors nut later long-term gains are largely from

the result of muscle hypertrophy

neural adaptations always accompany

the strength gains that result from resistance training, but hyoertrophy may or may not take place

with traditional training methods, an intensity of 60-80% of 1RM or higher is needed

to achieve substantial increases in muscle size HOWEVERRRR more recent research has suggested that low-intensity exercise at <50% of 1RM can lead to gains in muscle size equal to those seen at high intensities

fibers tend to take on characteristics of the opposite fiber type if the training was of the opposite kind ex:

type II fibers might become more oxidative with aerobic training

with resistance training, there is a transition of type IIx to

type IIa fibers

With resistance training there is a transition of

type IIx to type IIa fibers

Muscles atrophy (decrease in size and strength)

when they become inactive, as with injury, immobilization, or cessation of training

Mechanisms of Muscle Strength Gain: Neural Control

•Anaerobic training may elicit adaptations along the neuromuscular chain, beginning in the higher brain centers and continuing down to the level of individual muscle fibers. -Strength gain can occur without hypertrophy -Property of motor system, not just muscle

transient hypertrophy

•Due to edema formation from plasma fluid aka the PUMP -Disappears within hours :(

Mechanisms of Muscle Strength Gain: Detraining

•Leads to decrease in 1RM -Strength losses can be regained (~6 weeks) -New 1RM matches or exceeds old 1RM •Once training goal met, maintenance resistance program prevents detraining -Maintain strength and 1RM Reduce training frequency

Mechanisms of Muscle Strength Gain:Immobilization

•Major changes after 6 h -Lack of muscle use causes reduced rate of protein synthesis -Initiates process of muscle atrophy •First week: strength loss of 3 to 4% per day - decrease Size/atrophy - decrease Neuromuscular activity •(Reversible) effects on types I and II fibers -Cross-sectional area decreases cell contents degenerate -Type I affected more than type II

Mechanisms of Muscle Strength Gain: Chronic Muscle Hypertrophy

•Maximized by -High-velocity eccentric training -Disrupts sarcomere Z-lines (protein remodeling) •Leading to "muscle damage" or "fiber protein remodeling" •Concentric training only may limit muscle hypertrophy, strength gains -Limits amount of "work/stress" being done leading to less fibers being utilized

Mechanisms of Muscle Strength Gain: Fiber Hypertrophy

•More myofibrils •More actin, myosin filaments •More sarcoplasm •More connective tissue

Mechanisms of Muscle Strength Gain: Autogenic Inhibition

•Normal intrinsic inhibitory mechanisms -Golgi tendon organs -Inhibit muscle contraction if tendon tension too high -Protective mechanism •Training can decrease inhibitory impulses -Muscle can generate more force -May also explain superhuman feats of strength

Mechanisms of Muscle Strength Gain: Motor Unit Recruitment

•Normally motor units are not recruited all at the same time --> Size Principle -Excitatory impulses > inhibitory impulses •Synchronous recruitment may lead to strength gains -May produce more forceful contraction -Improves rate of force development - increase in capability to exert steady forces •Resistance training leads to synchronous recruitment

Mechanisms of Muscle Strength Gain:Motor Unit Rate Coding

•Rate coding refers to the motor unit firing rate. -Active motor units can discharge at higher frequencies to generate greater tensions. -Smaller muscles (e.g., first dorsal interosseous) rely more on rate coding

Mechanisms of Muscle Strength Gain:Atrophy and Inactivity

•Reduction or cessation of activity causes major change in muscle structure and function •Limb immobilization studies •Detraining studies

Interaction Between Resistance Training and Diet

•Resistance training increases protein synthesis •20-25 grams of protein after resistance exercise for muscle growth •1.6-1.7 grams protein / kg body weight / day for increasing muscle mass •Small doses (20 g) every 2-3 hours are recommended for protein synthesis

Mechanisms of Muscle Strength Gain:Neural Activation and Hypertrophy

•Short-term increase in muscle strength -Substantial increase in 1RM -Due to increase in voluntary neural activation -Neural factors critical in first 8 to 10 weeks • •Long-term increase in muscle strength -Associated with significant fiber hypertrophy -Net increase in protein synthesis takes time to occur -Hypertrophy major factor after first 10 weeks

Resistance Training for Sport

•Training beyond basic strength, power, and endurance needs of the sport not worth it •Training costs valuable time •Training results should be tested with sport-specific performance metric

Mechanisms of Muscle Strength Gain: Fiber Type Alterations

•Training regimen may not outright change fiber type, but -Type II fibers become more oxidative with aerobic training -Type I fibers become more anaerobic with anaerobic training •Fiber type conversion possible under certain conditions -Cross-innervation -Chronic low-frequency stimulation -High-intensity treadmill or resistance training